Check that a haploid product contains one of each chromosome type
A normal single-set product contains each required chromosome type once.
Section 17.3 · Meiosis
Exam scope and assessment notes
Extended only (Supplement) · Biology 0970, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked; human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0970 has the same subject content as IGCSE 0610, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Recall chromosomes, genes and alleles, complete chromosome sets, mitosis and fusion of gamete nuclei.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What must one complete three-type set contain?
What you will learn
- Use a reference set to check chromosome identity
- Distinguish a complete set from an arbitrary half-count
Original teaching model. Counts, source combinations and sample records are stipulated; drawings are schematic.
| Feature | Meaning |
|---|---|
| Diploid reference | 1A/1B, 2A/2B, 3A/3B |
| Complete product | 1A, 2B, 3A: types 1, 2 and 3 |
| Same count but incomplete | 1A, 1B, 2A: type 3 is missing |
| Source labels | A and B denote contributions, not allele dominance |
Use a reference set to check chromosome identity
Halving the chromosome number is not enough to describe a normal haploid complement when chromosome identities are supplied. In a three-type model, the reference set contains types one, two and three. A diploid precursor has a corresponding pair of each type. A normal haploid product contains one representative of each type, so it contains three chromosomes in one complete set.
Use source labels separately from type labels. The precursor may contain 1A and 1B, 2A and 2B, and 3A and 3B. Here A and B identify the two corresponding source contributions; they are not dominant and recessive alleles. A product containing 1A, 2B and 3A is complete. Another containing 1B, 2A and 3B is also complete even though its source combination differs.
Distinguish a complete set from an arbitrary half-count
A supplied product containing 1A, 1B and 2A still has three chromosomes, but it has two of type one and no type three. Its count is half of six, yet it does not meet the stipulated normal single-set pattern. The two checks are complementary: calculate the number and examine the required chromosome types. The labels are an original model, not a measured human chromosome analysis.
Do not infer a clinical outcome from an incomplete model complement. The purpose of the task is to explain why normal reduction means one complete set, not any arbitrary half of the objects. A colour or letter cannot by itself establish every gene sequence, chromosome condition or ability to become a functional gamete. Apply only the explicit reference set and evidence supplied in the question.
Pause and explain
Which product is complete in the stated model?
Worked example
Reference types are 1, 2 and 3. Compare 1A/2B/3A with 1A/1B/2A.
Show the worked solution
- Both products contain three labelled chromosomes.
- The first includes every required type once.
- The second repeats type one and omits type three.
Answer Only 1A/2B/3A is a complete single-set complement in this stipulated model; equal counts do not establish equal completeness.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
The reference types are 1, 2 and 3. Check product 1B/2A/3B for count and completeness.
Give me a hint
Ignore source letters when checking the required types.
Compare my reasoning
- Count three chromosomes.
- Check one of each reference type.
It has three chromosomes and one of every required type, so it is a complete haploid complement in this stipulated normal model.
Look for these in your work
- Three chromosomes
- Types one two and three each represented once
Compare 1A/1B/2B with 1A/2B/3B. Both have three chromosomes. Which meets the normal one-set requirement and why?
Give me a hint
Look for duplicated and missing types.
Compare my reasoning
- List the types in each product.
- Identify the missing type in the first.
- Choose the complete product.
1A/2B/3B meets the requirement. The first has two type-one chromosomes and no type three, so an equal count does not make it complete.
Look for these in your work
- Selects the second product
- Explains duplication and missing type three
A colour diagram shows three different-coloured chromosome rods. Explain what extra information you need before claiming a complete haploid set.
Give me a hint
Colours must have a stated meaning and a reference complement.
Compare my reasoning
- Request a key connecting colours with chromosome types.
- Request the species or stipulated single-set complement.
- Compare identities with the reference.
A key and the reference single-set complement are needed. Different colours alone do not prove that all required chromosome types are present once, or establish every DNA sequence or gamete function.
Look for these in your work
- Requires key and reference set
- Limits claims from colour alone
Common mistakes
- Calling any three of six chromosomes a normal haploid set
- Reading source labels A and B as dominance labels
- Inferring clinical consequences from a schematic
What can you explain now?
Which product is complete in the stated model?
Compare with the explanation
1A 2B 3A
It contains one chromosome of each required type.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Without your notes, use a reference set to check chromosome identity and distinguish a complete set from an arbitrary half-count. State the chromosome number per nucleus and distinguish chromosome-set reduction from fertilisation.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.